The present invention relates to machine tools, and more particularly to devices for finishing shaped surfaces with an abrasive tool. The invention may be used most successfully for finishing shaped surfaces of gas and steam turbine blades. The device of the present invention may be used, particularly, on transverse circular milling machines for finishing (dimensionless) of turbine blades preliminarily machined on the same machine tools.
One of the main unsolved problems in manufacturing powerful steam and gas turbines is the problem concerning mechanised finishing of shaped surfaces of blades having a variable profile. In the world practice most of the large blades are ground with manual grinding devices. The process is unproductive, harmful to health, and it fails to ensure the stability of dimensions and of the quality of the machined surfaces. High contact temperature in the process of grinding gives rise to stresses in the surface layer reaching 40 kg/mm.sup.2, to burned local surface areas and to microcracks.
Known in the art is a device for finishing blade surfaces comprising an abrasive tool secured on a lever and spring-urged to the surface being machined. The tool reciprocates relative to the blade surface being machined and the blade rotates about its axis. Besides, the blade may be moved in two mutually perpendicular directions, the movement being effected from a copying mechanism.
A disadvantage of this device consists in the fact that it machines only the outer shaped surface of the blade and fails to machine the inner shaped surface of the blade because the tool cannot be accommodated at the inner surface.
Another known device for machining spherical surfaces comprises a fixed base with a carriage mounted on it. The carriage performing a reciprocating motion along the generatrix of the work-piece being machined, while the latter rotates about its axis. The carriage is provided with a hinged support for a pivoting double-arm lever. The pivoting axis of the lever is parallel to the direction in which the carriage moves. One arm of the lever carries an abrasive tool.
The reciprocating motion of the carriage is brought about by a drive mechanism consisting of a rotating drive shaft and of an eccentric mechanism coupled to the carriage. The carriage is spring-urged thereby providing for the abrasive tool to be urged to the surface being machined.
A disadvantage of the above-mentioned device consists in the fact that it machines only surfaces of workpieces having the shape of bodies of rotation. When such devices are used for finishing workpieces which do not have the shape of bodies of rotation, such a device wouldn't ensure a permanent effect of urging of the tool to the surface being machined, because the effect of urging in this case would not be normal to the surface being machined at any point of contact with the tool.